Are we normal or average?

In the last few weeks I have gotten some questions and comments about using the term “normal”. In the field of applied climatology, the word “normal” has a specific meaning and refers to 30-year averages that are updated every decade. Currently we are using the 1981-2010 period for those calculations. Normals are one of the tools of trade for providing a benchmark or reference point to compare conditions at a particular time or to compare two or more stations. Other averaging periods or statistical methods can be employed in their place. For example, some utilities use a 10-year running average, updated every year, in their work. In some instances, especially if the distribution is not normally distributed, the median, or selected percentiles, may be more appropriate.

If you pull up dictionary.com or look in Webster’s Dictionary, the noun “normal” is defined as the mean or average. So in that sense, “normal”, “mean”, and “average” refer to the same thing.

Many people think of the adjective form of the word “normal”, which  means that it is the most common or usual case. However, the 30-year averages were not intended to be viewed that way. In fact, I sometimes joke that it is abnormal to be normal on the rare occasion when the temperature or precipitation exactly matches the normal value.

A more mundane issue is that in writing this blog I often report things like “the statewide average temperature was 2.3 degrees above normal”. If I used the word average instead of normal, it would be “the statewide average temperature was 2.3 degrees above average” which sounds very close to saying “the  … average was … above average”.

Or I could always use the longer and more complete term “the 30-year average updated every 10 years” in place of “normal”. While it is more precise, it gets to be awkward at times. Right now I’m leaning towards continuing with “normal” but give an explanation somewhere at the bottom of the post. This morning on the drive in I decided to try “long-term average” and see how that works.

About Jim Angel

I have been the state climatologist for Illinois since 1997 and have worked at the Illinois State Water Survey since 1984.
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One Response to Are we normal or average?

  1. gator69 says:

    Hey Jim! I would say you are ‘above average’. I appreciate you entertaining my thoughts and comments, and I look forward to your future posts.

    All the best.

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